1. Field of the Invention:
The invention relates to circuit breakers and, more particularly, to circuit breakers having an automatic overcurrent trip capability and a manually operable shunt trip capability.
2. Description of the Prior Art:
A circuit breaker having an operating mechanism of the type herein disclosed is described in U.S. Pat. No. 3,808,567 issued Apr. 30, 1974 to Alfred E. Maier and assigned to the assignee of the present invention. A circuit breaker including a manually operable shunt trip device is described in the aforementioned copending U.S. Pat. application Ser. No. 605,372 (W.E. 45,633). The shunt trip device described therein includes a source of control voltage connected through a cut-off switch to a bridge rectifier circuit connected in parallel with the trip coil of the circuit breaker and the output of the solid state overcurrent tripping circuits. This arrangement is well suited to lower control voltages in the range of 32 to 120 volts, usually supplied through a stepdown transformer. The transformer produces a filtering effect which provides suppression of overvoltage spikes and other noise components of the control voltage. It would be desirable to operate the shunt trip device of a circuit breaker directly from higher line voltages of, for example, 600 volts without the use of a stepdown transformer. However, this would require a much higher rating bridge rectifier device which is expensive and which would be susceptible to damage from overvoltage spikes. It would be desirable, therefore, to provide a low cost shunt trip device for operating the trip coil of a circuit breaker which is directly operable from higher line voltages without the use of a stepdown transformer, while providing protection to the trip coil and the solid state overcurrent trip circuit.